Why standard definition rarely looks good on a HDTV display

November 16, 2004

colorbarsA few months ago my girlfriend and I were watching a little Voom and she remarked, “Why do the regular stations look worse than before?” Regular stations meaning non-HD and before meaning on the old standard definition television, I used to have. Being the pseudo technophile I am, I shot back “Well they’re not high definition stations baby, they don’t have as much resolution.” When the words came out of my mouth, I was comfortable enough to leave it at that.

Later, however I began to wonder if there was more to it than that. I mean it sounds plausible enough, right? Well, maybe not. While resolution is obviously a major factor in the eye’s interpretation of what “looks good”, NTSC and ATSC differ in more than just resolution. Not to over simplify the “digital” difference, but NTSC is an analog signal while ATSC (digital television) is well…digital. A byproduct of this is the color information is digitally ‘set’ in the signal. Short of total signal dropout, the DTV image will always have that inherent correctness to it that an analog signal may not. The color information in an analog signal can and often does vary, as transmission encoding and decoding tends to alter it.


Another way to think of it is analog (NTSC) television uses amplitude modulation (AM) to transmit the video and frequency modulation (FM) to transmit the audio. This alone introduces some inherent flaws and wavering in color quality. While digital satellite is indeed a digital signal, older analog stations that are shown on DBS and digital cable systems still originate in the analog domain, while DTV does not. Its signal never leaves the digital path thereby keeping a constant or closer to constant color level. Also NTSC was never really intended for the mondo sized televisions we watch today. You have to remember when color television got it’s foothold in the late 1960’s, a 20” TV was considered large. And as always the bigger the screen size grows, the flaws in the image become more apparent.

Add in any other artifacts, such as signal interference or compression from digital cable or satellite, and you’ll see those artifacts quite clearly. Digital cable and DBS satellite both use digital compression to fit more channels in a fixed amount of space. The level of compression varies by channel and content, but in the race to have “more channels”, image quality noticeably suffered. Compression artifacts include “macroblock” blockness and overly soft pictures. Some satellite channels are compressed at a resolution of 480×480 (or lower!) instead of 720×480 (like a DVD), and this results in a soft picture.

Another factor to consider is the aspect ratio itself. Unless you watch 4:3 programming with pillar boxes, the images have to be stretched to fill today’s widescreen displays. This can easily distort the image and add flaws, sans sets with high quality internal scaler’s. Yet another factor to consider is “digital CATV” itself. Granted most cable TV providers transmit hi-def digital programming on the higher channels, but many of the older standard definition channels found in the lower band are still sent analog. That’s right, just because you have digital cable doesn’t mean every channel is true digital. Add native resolution scaling to this and it’s not hard at all to end up with a significantly worse image than you had to begin with.

Looking forward:
In the past, television lived by a few simple rules. It was 4:3 and for the most part followed the NTSC standard. Once digital television, rather HDTV, came on the scene we had a few more ingredients in the soup. Manufacturers still had to honor older legacy products and of course at the same time support the new digital format. Now we have displays that are native 720p or 1080i while much of the programming is still 480i, although with time this will dissipate. It’s likely that just announcing ‘analog TV is gone, get a new set’ would have made the transition much less demanding technically. However consumers would have never stood for this and it would have caused massive confusion, anger, and resentment. Hopefully however it won’t be too much longer before the majority of channels are broadcast in pure, unadulterated high definition or at least we can cross our fingers.



Posted by Bryan Greenway | | Filed Under HDTV Programming


Comments

  • B.Greenway

    I don’t think this is a situation where one individual subscriber is immediately going to see 200 new channels, I think that’s spread over at least two different satellites, maybe more and probably split up into regions, such as Fox’s regional sports. I think Voom is fully aware they can’t afford to mess up the things they already do well.

  • B.Greenway

    I don’t think this is a situation where one individual subscriber is immediately going to see 200 new channels, I think that’s spread over at least two different satellites, maybe more and probably split up into regions, such as Fox’s regional sports. I think Voom is fully aware they can’t afford to mess up the things they already do well.

  • jose4

    I have found that SD TV on, say, Voom, is of better (less soft) PQ than on Echostar or DirecTV (which aren’t watchable on a big set). Comparing side-to-side broadcasts of an analog C-band signal and its digital counterpart on Voom, on a television that allows running and SD signal through compononent cables, the analog signal is not noticeably better through S-video C-band.

    I write this because later in the blog you mention Voom’s plans to add “200 SD channels.” If these are the overcompressed signals already being sent by the two major DBS players, this is not good news to the home theater (read big TV) owner, is it?

  • jose4

    I have found that SD TV on, say, Voom, is of better (less soft) PQ than on Echostar or DirecTV (which aren’t watchable on a big set). Comparing side-to-side broadcasts of an analog C-band signal and its digital counterpart on Voom, on a television that allows running and SD signal through compononent cables, the analog signal is not noticeably better through S-video C-band.

    I write this because later in the blog you mention Voom’s plans to add “200 SD channels.” If these are the overcompressed signals already being sent by the two major DBS players, this is not good news to the home theater (read big TV) owner, is it?

  • I hear you on the difference… as you’ve alluded to the digital version of the channel is far superior as it comes through in pure digital goodness.

    When watching a broadcast not in HD, the difference is staggering between my 2 options for the same network. The HD version of the same channel is so much more clear than the show broadcast on the original non-HD channel. I just wish in addition to actually rolling out HD, there was a standard for what kind of HD. It’s quite annoying to see my cable box have to cycle through display types to get to the right one for my TV.

    Fox likes 720p, CBS seems to do 1080i etc…

  • I hear you on the difference… as you’ve alluded to the digital version of the channel is far superior as it comes through in pure digital goodness.

    When watching a broadcast not in HD, the difference is staggering between my 2 options for the same network. The HD version of the same channel is so much more clear than the show broadcast on the original non-HD channel. I just wish in addition to actually rolling out HD, there was a standard for what kind of HD. It’s quite annoying to see my cable box have to cycle through display types to get to the right one for my TV.

    Fox likes 720p, CBS seems to do 1080i etc…